The use of a fluidized bed reactor for the incineration of refuse, such as municipal and industrial wastes, in the form of sludge is generally known and involves the burning of sludge with air while fluidizing it in a fluidized bed. In order to improve the combustion along with the fluidizing of the sludge, a bed make-up material such as sand or clay with limestone are fed together with the sludge to the fluidized bed.
A typical type of fluidized bed reactor is equipped with a plurality of air diffuser tubes or plates in the lower section of the reactor body, and the upper section of the reactor body is equipped with a sludge feeding unit and a bed make-up material feeding unit. The sludge is burned while both the sludge and the bed make-up material are fluidized by primary air which is blown out through the air diffusers.
As the organic compounds are decomposed and burned within the fluidizing bed, the incombustibles descend along with the fluidizing medium down through the reactor and pass through the gaps between the air diffuser tubes in the lower section of the fluidizing bed. The fluidizing medium is separated from the combustion residue, and is returned to the fluidized bed.
The sludge is generally of low calorie content and contains high concentrations of volatile organic compounds, salt, and moisture. As the sludge is fed to the fluidizing bed, the volatile organic compounds are decomposed to generate pyrolytic gases, and the incombustible substances and ash are left in the form of particulate material. In addition, sludge has substantial adhesive properties and since the sludge is deposited directly on the fluidized bed, it is quickly dried, decomposed and ignited which can lead to the formation of ash agglomerations resulting in frequency reactor shutdown.
Further, as the concentration of volatile organic compounds can vary substantially from batch to batch, and even within a single batch of sludge, it is difficult to maintain stable combustion which results in unacceptable emissions of hazardous and toxic gases. Further, the unregulated burning of sludge can result in the formation of highly corrosive gases, such as HCl, HBr etc., as well as, the creation of low oxidation states of metals which are environmentally hazardous. As a result, the typical fluidized bed reactor of this type is incapable of meeting all of the Environmental Protection Agency's (EPA's) stringent emission requirements for compounds, such as SOx, NOx, CO, VOC, and dioxin, as well as EPA specifications for gas temperature and gas retention time required for the destruction of toxic gases.